lvgl/docs/overview/animation.md

.. include:: /header.rst 
:github_url: |github_link_base|/overview/animation.md

Animations

You can automatically change the value of a variable between a start and an end value using animations. The animation will happen by periodically calling an "animator" function with the corresponding value parameter.

The animator functions have the following prototype:

void func(void * var, lv_anim_var_t value);

This prototype is compatible with the majority of the set functions of LVGL. For example lv_obj_set_x(obj, value) or lv_obj_set_width(obj, value)

Create an animation

To create an animation an lv_anim_t variable has to be initialized and configured with lv_anim_set_...() functions.

/* INITIALIZE AN ANIMATION
 *-----------------------*/

lv_anim_t a;
lv_anim_init(&a);

/* MANDATORY SETTINGS
 *------------------*/

/*Set the "animator" function*/
lv_anim_set_exec_cb(&a, (lv_anim_exec_xcb_t) lv_obj_set_x); 

/*Set the "animator" function*/
lv_anim_set_var(&a, obj); 

/*Length of the animation [ms]*/
lv_anim_set_time(&a, duration);

/*Set start and end values. E.g. 0, 150*/
lv_anim_set_values(&a, start, end);

/* OPTIONAL SETTINGS
 *------------------*/

/*Time to wait before starting the animation [ms]*/
lv_anim_set_delay(&a, delay);

/*Set path (curve). Default is linear*/
lv_anim_set_path(&a, lv_anim_path_ease_in);

/*Set a callback to call when animation is ready.*/
lv_anim_set_ready_cb(&a, ready_cb);

/*Set a callback to call when animation is started (after delay).*/
lv_anim_set_start_cb(&a, start_cb);

/*Play the animation backward too with this duration. Default is 0 (disabled) [ms]*/
lv_anim_set_playback_time(&a, wait_time); 

/*Delay before playback. Default is 0 (disabled) [ms]*/
lv_anim_set_playback_delay(&a, wait_time);

/*Number of repetitions. Default is 1.  LV_ANIM_REPEAT_INFINIT for infinite repetition*/
lv_anim_set_repeat_count(&a, wait_time);

/*Delay before repeat. Default is 0 (disabled) [ms]*/
lv_anim_set_repeat_delay(&a, wait_time);

/*true (default): apply the start vale immediately, false: apply start vale after delay when then anim. really starts. */
lv_anim_set_early_apply(&a, true/false);

/* START THE ANIMATION
 *------------------*/
lv_anim_start(&a);                             /*Start the animation*/

You can apply multiple different animations on the same variable at the same time. For example, animate the x and y coordinates with lv_obj_set_x and lv_obj_set_y. However, only one animation can exist with a given variable and function pair. Therefore lv_anim_start() will delete the already existing variable-function animations.

Animation path

You can determinate the path of animation. The most simple case is linear, meaning the current value between start and end is changed with fixed steps. A path is a function which calculates the next value to set based on the current state of the animation. Currently, there are the following built-in paths functions:

• lv_anim_path_linear linear animation
• lv_anim_path_step change in one step at the end
• lv_anim_path_ease_in slow at the beginning
• lv_anim_path_ease_out slow at the end
• lv_anim_path_ease_in_out slow at the beginning and at the end
• lv_anim_path_overshoot overshoot the end value
• lv_anim_path_bounce bounce back a little from the end value (like hitting a wall)

Speed vs time

By default, you set the animation time. But in some cases, setting the animation speed is more practical.

The lv_anim_speed_to_time(speed, start, end) function calculates the required time in milliseconds to reach the end value from a start value with the given speed. The speed is interpreted in unit/sec dimension. For example, lv_anim_speed_to_time(20,0,100) will yield 5000 milliseconds. For example, in case of lv_obj_set_x unit is pixels so 20 means 20 px/sec speed.

Delete animations

You can delete an animation with lv_anim_del(var, func) if you provide the animated variable and its animator function.

Examples

.. include:: ../../examples/anim/index.rst

API

.. doxygenfile:: lv_anim.h
  :project: lvgl